Polymorphic playback system with switching oscillation prevention

ABSTRACT

A polymorphic playback system in which one or more parameters of a signal path of the polymorphic playback system are varied based on one or more characteristics of a playback signal processed by the signal path may include a control subsystem configured to detect an out-of-band noise profile of the playback signal and set one or more playback signal magnitude thresholds for switching between polymorphic modes of the polymorphic playback system based on the out-of-band noise profile, wherein the polymorphic modes comprise at least a first polymorphic mode in which one or more first parameters are applied to the signal path and a second polymorphic mode in which one or more second parameters are applied to the signal path.

FIELD OF DISCLOSURE

The present disclosure relates in general to circuits for audio devices,including without limitation personal audio devices, such as wirelesstelephones and media players, and more specifically, to systems andmethods for preventing oscillation or frequent switching betweenpolymorphic modes of a polymorphic playback system.

BACKGROUND

Personal audio devices, including wireless telephones, such asmobile/cellular telephones, cordless telephones, mp3 players, and otherconsumer audio devices, are in widespread use. Such personal audiodevices may include circuitry for driving a pair of headphones or one ormore speakers. Such circuitry often includes a power amplifier fordriving an audio output signal to headphones or speakers.

A personal audio device may include a polymorphic playback system. Apolymorphic playback system may include a playback system in which oneor more parameters of a signal path of the playback system are variedbased on one or more characteristics of a playback signal processed bythe signal path. Examples of a polymorphic playback system include adynamic range enhancement playback system in which signal gains of aplayback path are varied based on one or more characteristics (e.g.,signal magnitude) of the playback signal, a multiple processing pathplayback system in which a processing path for processing the playbacksignal is selected based on one or more characteristics (e.g., signalmagnitude) of the playback signal, an amplifier with a configurableoutput stage (e.g., configurable as a Class AB output stage or Class Doutput stage) in which the configuration of the output stage is based onone or more characteristics (e.g., signal magnitude) of the playbacksignal, or any other suitable polymorphic playback system.

Many playback systems, such as those that perform adaptive noisecancellation, are required to have low latency in their playback paths.In addition, many playback systems include playback signals with asignificant amount of out-of-band noise. In some instances, the presenceof out-of-band noise may cause switching of a polymorphic playbacksystem from a first polymorphic mode in which a first set of one or moreparameters are applied to the signal path based on one or morecharacteristics of a playback signal to a second polymorphic mode inwhich a second set of one or more parameters are applied to the signalpath based on the one more characteristics of a playback signal, andvice versa. In some instances, such out-of-band noise may lead tofrequent switching or oscillation between the polymorphic modes. Suchfrequent switching may occur because thresholds in a control subsystemfor switching between modes may be optimized for a particular datasource. However, if the data source is changed, or its noise performancedrifts over time, noise fluctuation may cause random crossing of theswitching threshold and thus, oscillation between polymorphic modes.

Such out-of-band noise may influence an in-band signal received by alevel detector for detecting a playback signal magnitude in apolymorphic playback system that utilizes the playback signal magnitudeas a characteristic for setting one or more parameters of the signalpath of the playback system. While a strong low-pass filter could beused to filter out the out-of-band noise, use of a strong low-passfilter may add too much undesirable latency to signal detection.

SUMMARY

In accordance with the teachings of the present disclosure, one or moredisadvantages and problems associated with existing approaches tofrequent switching between polymorphic modes in a polymorphic playbacksystem may be reduced or eliminated.

In accordance with embodiments of the present disclosure, a polymorphicplayback system in which one or parameters of a signal path of thepolymorphic playback system are varied based on one or morecharacteristics of a playback signal processed by the signal path mayinclude a control subsystem configured to detect an out-of-band noiseprofile of the playback signal and set one or more playback signalmagnitude thresholds for switching between polymorphic modes of thepolymorphic playback system based on the out-of-band noise profile,wherein the polymorphic modes comprise at least a first polymorphic modein which one or more first parameters are applied to the signal path anda second polymorphic mode in which one or more second parameters areapplied to the signal path.

In accordance with these and other embodiments of the presentdisclosure, a method may be provided for use in a polymorphic playbacksystem in which one or more parameters of a signal path of thepolymorphic playback system are varied based on one or morecharacteristics of a playback signal processed by the signal path, themethod comprising detecting an out-of-band noise profile of the playbacksignal and setting one or more playback signal magnitude thresholds forswitching between polymorphic modes of the polymorphic playback systembased on the out-of-band noise profile, wherein the polymorphic modescomprise at least a first polymorphic mode in which one or more firstparameters are applied to the signal path and a second polymorphic modein which one or more second parameters are applied to the signal path.

Technical advantages of the present disclosure may be readily apparentto one skilled in the art from the figures, description and claimsincluded herein. The objects and advantages of the embodiments will berealized and achieved at least by the elements, features, andcombinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are examples and explanatory and arenot restrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 is an illustration of an example personal audio device, inaccordance with embodiments of the present disclosure;

FIG. 2A illustrates a block diagram of selected components of an exampleaudio integrated circuit of a personal audio device, in accordance withembodiments of the present disclosure;

FIG. 2B illustrates a block diagram of selected components of anotherexample audio integrated circuit of a personal audio device, inaccordance with embodiments of the present disclosure;

FIG. 3 illustrates a block diagram of selected components of an exampleamplifier, in accordance with embodiments of the present disclosure;

FIG. 4 illustrates a block diagram of selected components of a digitalmicrophone integrated circuit, in accordance with embodiments of thepresent disclosure;

FIG. 5A illustrates a block diagram of selected components of ageneralized polymorphic playback system, in accordance with embodimentsof the present disclosure; and

FIG. 5B illustrates a block diagram of selected components of anothergeneralized polymorphic playback system, in accordance with embodimentsof the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is an illustration of an example personal audio device 1, inaccordance with embodiments of the present disclosure. FIG. 1 depictspersonal audio device 1 coupled to a headset 3 in the form of a pair ofearbud speakers 8A and 8B. Headset 3 depicted in FIG. 1 is merely anexample, and it is understood that personal audio device 1 may be usedin connection with a variety of audio transducers, including withoutlimitation, headphones, earbuds, in-ear earphones, and externalspeakers. A plug 4 may provide for connection of headset 3 to anelectrical terminal of personal audio device 1. Personal audio device 1may provide a display to a user and receive user input using a touchscreen 2, or alternatively, a standard liquid crystal display (LCD) maybe combined with various buttons, sliders, and/or dials disposed on theface and/or sides of personal audio device 1. As also shown in FIG. 1,personal audio device 1 may include an audio integrated circuit (IC) 9for generating an analog audio signal for transmission to headset 3and/or another audio transducer.

FIG. 2A illustrates a block diagram of selected components of an exampleaudio IC 9A of a personal audio device, in accordance with embodimentsof the present disclosure. In some embodiments, example audio IC 9A maybe used to implement audio IC 9 of FIG. 1. As shown in FIG. 2A, amicrocontroller core 18 may supply a digital audio input signal DIG_INto a digital-to-analog converter (DAC) 14, which may convert the digitalaudio input signal to an analog input signal V_(IN). DAC 14 may supplyanalog input signal V_(IN) to an amplifier 16A which may amplify orattenuate analog input signal V_(IN) to provide an audio output signalV_(OUT), which may operate a speaker, headphone transducer, a line levelsignal output, and/or other suitable output.

FIG. 2B is a block diagram of selected components of an example audio IC9B of a personal audio device, in accordance with embodiments of thepresent disclosure.

Example audio IC 9B of FIG. 2B may be similar in many respects toexample audio IC 9A of FIG. 2A, except as otherwise described herein. Asshown in FIG. 2B, a microcontroller core 18 may supply a digital audioinput signal DIG_IN to a digital gain element 12 to apply a selectabledigital gain x selected by control subsystem 20 to digital input signalDIG_IN. The amplified digital audio input signal may be communicated toa digital-to-analog converter (DAC) 14, which may convert the digitalaudio input signal to an analog input signal V_(IN). Together, digitalgain element 12 and DAC 14 may be referred to herein as a digital pathportion of the signal path from the input node for digital audio inputsignal DIG_IN to the output node for audio output signal V_(OUT)depicted in FIG. 2B. In the relevant art, digital gain element 12 andDAC 14 may sometimes be referred to as an audio compressor.

DAC 14 may supply analog input signal V_(IN) to an amplifier 16B whichmay amplify or attenuate analog input signal V_(IN) in conformity with aselectable analog gain k/x to provide an audio output signal V_(OUT),which may operate a speaker, headphone transducer, a line level signaloutput, and/or other suitable output Amplifier 16B may be referred toherein as an analog path portion of the signal path from the input nodefor digital audio input signal DIG_IN to the output node for outputvoltage signal V_(OUT) depicted in FIG. 2B. In the relevant art,amplifier 16B may sometimes be referred to as an audio expander.

As shown in FIG. 2B, audio IC 9B may include a control subsystem 20configured to, based on one or more characteristics of digital audioinput signal DIG_IN, control selectable digital gain x of gain element12 and a selectable analog gain k/x of amplifier 16B. In embodiments inwhich a volume control is present, a volume control signal may beprovided from a microcontroller or other digital control circuitresponsive to a user interface, volume knob encoder or program command,or other suitable mechanism.

As an example of the dynamic range enhancement functionality of audio IC9B, when digital audio input signal DIG_IN is at or near zero decibels(0 dB) relative to the full-scale voltage of the digital audio inputsignal, control subsystem 20 may select a first digital gain (e.g., x₁)for the selectable digital gain and a first analog gain (e.g., k/x₁) forthe selectable analog gain. However, if the magnitude of digital audioinput signal DIG_IN is below a particular predetermined thresholdmagnitude relative to the full-scale voltage of digital audio inputsignal DIG_IN (e.g., −20 dB), control subsystem 20 may select a seconddigital gain (e.g., x₂) greater than the first digital gain (e.g.,x₂>x₁) for the selectable digital gain and a second analog gain (e.g.,k/x₂) lesser than the first analog gain (e.g., k/x₂<k/x₁) for theselectable analog gain. In each case, the cumulative path gain (e.g., k)of the selectable digital gain and the selectable analog gain may besubstantially constant (e.g., the same within manufacturing and/oroperating tolerances of audio IC 9B). In some embodiments, k may beapproximately equal to 1, such that the cumulative path gain is a unitygain. Such modification of digital gain and analog gain may increase thedynamic range of audio IC 9B compared to approaches in which the digitalgain and analog gain are static, as it may reduce the noise injectedinto audio output signal V_(OUT), which noise may be a generallymonotonically increasing function of the analog gain of amplifier 16B.While such noise may be negligible for higher magnitude audio signals(e.g., at or near 0 dB relative to full-scale voltage), the presence ofsuch noise may become noticeable for lower magnitude audio signals(e.g., at or near −20 dB or lower relative to full-scale voltage). Byapplying a smaller analog gain at amplifier 16B for smaller signalmagnitudes, the amount of noise injected into audio output signalV_(OUT) may be reduced, while the signal level of audio output signalV_(OUT) may be maintained in accordance with the digital audio inputsignal DIG_IN through application of a digital gain to gain element 12inversely proportional to the analog gain.

FIG. 3 illustrates a block diagram of selected components of an exampleamplifier 18, in accordance with embodiments of the present disclosure.In some embodiments, amplifier 18 may be used to implement all or aportion of amplifier 16A of FIG. 2A. In these and other embodiments,amplifier 18 may be used to implement all or a portion of amplifier 16Bof FIG. 2B.

As shown in FIG. 3, amplifier 18 may include a first stage 22 (e.g., ananalog front end) configured to receive analog input signal V_(IN) at anamplifier input of amplifier 18 and generate an intermediate signalV_(INT) which is a function of analog input signal V_(IN), a finaloutput stage 24 configured to generate audio output signal V_(OUT) at anamplifier output of amplifier 18 as a function of intermediate signalV_(INT), a signal feedback network 26 coupled between the amplifieroutput and the amplifier input, and a control subsystem 28 forcontrolling the operation of certain components of amplifier 18, asdescribed in greater detail below.

First stage 22 may include any suitable analog front end circuit forconditioning analog input signal V_(IN) for use by final output stage24. For example, first stage 22 may include one or more analogintegrators 32 cascaded in series, as shown in FIG. 3.

Final output stage 24 may include any suitable driving circuit fordriving audio output signal V_(OUT) as a function of intermediate signalV_(INT) (thus, also making audio output signal V_(OUT) a function ofanalog input signal V_(IN)) wherein final output stage 24 is switchableamong a plurality of modes including at least a first mode in whichfinal output stage 24 generates audio output signal V_(OUT) as amodulated output signal which is a function of intermediate signalV_(INT) and a second mode in which final output stage 24 generates audiooutput signal V_(OUT) as an unmodulated output signal which is afunction of intermediate signal V_(INT). To carry out thisfunctionality, final output stage 24 may include a class-D audio outputstage 42 which may be enabled in the first mode (and disabled in thesecond mode) to generate audio output signal V_(OUT) as a modulatedoutput signal which is a function of intermediate signal V_(INT) and aclass-AB audio output stage 44 which may be enabled in the second mode(and disabled in the first mode) to generate audio output signal V_(OUT)as an unmodulated output signal which is a function of intermediatesignal V_(INT).

Class-D audio amplifier 42 may comprise any suitable system, device, orapparatus configured to amplify intermediate signal V_(INT) and convertintermediate signal V_(INT) into a series of pulses by pulse widthmodulation, pulse density modulation, or another method of modulation,such that intermediate signal V_(INT) is converted into a modulatedsignal in which a characteristic of the pulses of the modulated signal(e.g., pulse widths, pulse density, etc.) is a function of the magnitudeof intermediate signal V_(INT). After amplification by class-D audioamplifier 42, its output pulse train may be converted back to anunmodulated analog signal by passing through a passive low-pass filter,wherein such low-pass filter may be inherent in output circuitry ofclass-D audio amplifier 42 or a load driven by final output stage 24. Asshown in FIG. 3, class-D audio amplifier 42 may include a control inputfor receiving a control input from control subsystem 28 in order toselectively enable class-D audio amplifier 42 during the first mode anddisable class-D audio amplifier 42 during the second mode (e.g., preventclass-D audio amplifier 42 from driving the amplifier output ofamplifier 18 by disabling or decoupling a supply voltage from class-Daudio amplifier 42 or by disabling or decoupling driving devices of theamplifier output of amplifier 18).

Class-AB audio amplifier 44 may comprise any suitable system, device, orapparatus configured to amplify intermediate signal V_(INT) with alinear gain and convert intermediate signal V_(INT) into an unmodulatedaudio output signal V_(OUT). As shown in FIG. 3, class-AB audioamplifier 44 may include a control input for receiving a control inputfrom control subsystem 28 in order to selectively enable class-AB audioamplifier 44 during the second mode and disable class-AB audio amplifier44 during the first mode (e.g., prevent class-AB audio amplifier 44 fromdriving the amplifier output of amplifier 18 by disabling or decouplinga supply voltage from class-AB audio amplifier 44 or by disabling ordecoupling driving devices of the amplifier output of amplifier 18).

In some embodiments, a signal gain (e.g., V_(OUT)/V_(INT)) of finaloutput stage 24 in the first mode may be approximately equal to thesignal gain of final output stage 24 in the second mode. In these andother embodiments, an offset (e.g., direct current offset) of finaloutput stage 24 in the first mode may be approximately equal to theoffset of final output stage 24 in the second mode.

Signal feedback network 26 may include any suitable feedback network forfeeding back a signal indicative of audio output signal V_(OUT) to theamplifier input of amplifier 18. For example, as shown in FIG. 3, signalfeedback network 26 may include variable feedback resistors 48, whereinresistances of variable feedback resistors 48 are controlled by controlsignals received from control subsystem 28, as described in greaterdetail below.

Control subsystem 28 may include any suitable system, device, orapparatus configured to receive information indicative of audio outputsignal V_(OUT), intermediate signal V_(INT), and/or other operationalcharacteristics of amplifier 18, and based at least thereon, controloperation of one or more components of amplifier 18. For example,control subsystem 28 may be configured to, based on a characteristic ofanalog input signal V_(IN) (e.g., which may be determined from receivingand analyzing intermediate signal V_(INT) and/or audio output signalV_(OUT)), switch between the first mode and the second mode of finaloutput stage 24. Such characteristic may include one or more of afrequency of analog input signal V_(IN), an amplitude of analog inputsignal V_(IN), a signal-to-noise ratio of analog input signal V_(IN), anoise floor of analog input signal V_(IN), or another noisecharacteristic of analog input signal V_(IN). For example, in someembodiments, control subsystem 28 may be configured to switch finaloutput stage 24 from the first mode to the second mode when an amplitudeof analog input signal V_(IN) decreases below a threshold amplitude, andmay be configured to switch final output stage 24 from the second modeto the first mode when an amplitude of analog input signal V_(IN)increases above the same threshold amplitude or another thresholdamplitude. In some embodiments, to reduce audio artifacts associatedwith switching between modes, control subsystem 28 may also beconfigured to switch between modes only when the amplitude of audiooutput signal V_(OUT) is approximately zero (e.g., when a modulatedsignal generated by class-D audio amplifier 42 is at its minimum voltagein its generated pulse train).

In addition, control subsystem 28 may also be configured to performcalibration of final output stage 24. For example, control subsystem 28may receive and analyze intermediate signal V_(INT) and audio outputsignal V_(OUT) to determine a gain of class-D audio amplifier 42 (e.g.,the signal gain of final output stage 24 in the first mode) and a gainof class-AB audio amplifier 44 (e.g., the signal gain of final outputstage 24 in the second mode), and based thereon, modify the gain ofclass-D audio amplifier 42 and/or the gain of class-AB audio amplifier44 in order to calibrate the signal gain of final output stage 24 in thesecond mode to match the signal gain of final output stage 24 in thefirst mode. As another example, control subsystem 28 may receive andanalyze intermediate signal V_(INT) and/or audio output signal V_(OUT)to determine an offset (e.g., direct current offset) of class-D audioamplifier 42 (e.g., the offset of final output stage 24 in the firstmode) and an offset of class-AB audio amplifier 44 (e.g., the offset offinal output stage 24 in the second mode), and based thereon, modify theoffset of class-D audio amplifier 42 and/or the offset of class-AB audioamplifier 44 in order to calibrate the offset of final output stage 24in the second mode to match the offset of final output stage 24 in thefirst mode.

In these and other embodiments, control subsystem 28 may also beconfigured to control characteristics of first stage 22 (e.g.,integrators 32) and/or signal feedback network 26. Control subsystem 28may maintain such characteristics and structure of first stage 22 andsignal feedback network 26 as static when switching between the firstmode and the second mode of final output stage 24 and when switchingbetween the second mode and the first mode. Maintaining thecharacteristics and structure of first stage 22 and signal feedbacknetwork 26 as static when switching between modes allows the modes toshare the same analog front end and feedback network, thus reducing orminimizing the likelihood of mismatched signal gain and offset betweenthe modes, and thus reducing or minimizing audio artifacts caused byswitching between modes. However, after control subsystem 28 hasswitched final output stage 24 to the second mode (e.g., amplifieroutput driven by class-AB amplifier 44), control subsystem 28 may modifycharacteristics of first stage 22 and/or signal feedback network 26 inorder to decrease a noise floor of amplifier 18. For example, in someembodiments, control subsystem 28 may modify characteristics ofintegrators 32 (e.g., resistances and/or capacitances of filtersinternal to integrators 32) and/or other components of first stage 22 inorder to decrease a noise floor of amplifier 18 when final output stage24 operates in the second mode. As another example, in these and otherembodiments, control subsystem 28 may modify characteristics of signalfeedback network 26 (e.g., resistances of variable feedback resistors48) in order to decrease a noise floor of amplifier 18 when final outputstage 24 operates in the second mode. When making such modification,control subsystem 28 may, before switching final output stage 24 fromthe second mode to the first mode, return such characteristics to theirunmodified states.

FIG. 4 illustrates a block diagram of selected components of a digitalmicrophone IC 52, in accordance with embodiments of the presentdisclosure. As shown in FIG. 4, digital microphone IC 52 may include twoor more audio processing paths 54 a and 54 b (which may be referred toherein individually as an audio processing path 54 and collectively asAFE/ADC paths 54), each AFE/ADC path 54 including a respective AFE 56(e.g., AFE 56 a, AFE 56 b) and a respective ADC (e.g., ADC 58 a, ADC 58b). An AFE 56 may receive an analog audio input signal ANALOG_IN via oneor more input lines which may allow for receipt of a single-endedsignal, differential signal, or any other suitable analog audio signalformat and may comprise any suitable system, device, or apparatusconfigured to condition analog audio input signal ANALOG_IN forprocessing by ADC 58. In some embodiments, analog audio input signalANALOG_IN may comprise an electronic signal generated by a microphone asa function of sound pressure incident upon the microphone. The output ofeach AFE 56 may be communicated to a respective ADC 58 on one or moreoutput lines.

An ADC 58 may comprise any suitable system, device, or apparatusconfigured to convert an analog audio signal received at its input, to adigital signal representative of analog audio input signal ANALOG_IN.ADC 58 may itself include one or more components (e.g., delta-sigmamodulator, decimator, etc.) for carrying out the functionality of ADC58.

A multiplexer 60 may receive a respective digital audio signal from eachof audio processing paths 54, and may select one of the digital audiosignals as the digital audio output signal DIGITAL_OUT based on acontrol signal generated by and communicated from a control subsystem64.

Driver 62 may receive the digital audio output signal DIGITAL_OUT outputby ADC 58 and may comprise any suitable system, device, or apparatusconfigured to condition such digital signal (e.g., encoding into AudioEngineering Society/European Broadcasting Union (AES/EBU), Sony/PhilipsDigital Interface Format (S/PDIF)), in the process generating digitalaudio output signal DIGITAL_OUT for transmission over a bus to a digitalaudio processor. In FIG. 4, the bus receiving digital audio outputsignal DIGITAL_OUT is shown as single-ended. In some embodiments, driver62 may generate digital audio output signal DIGITAL_OUT as adifferential digital audio output signal.

Control subsystem 64 may comprise any suitable system, device, orapparatus for selecting one of the digital audio signals output by thevarious audio processing paths 54 as digital audio output signalDIGITAL_OUT. In some embodiments, control subsystem 64 may make suchselection based on a magnitude of analog audio input signal ANALOG_IN ora signal derivative thereof. For example, control subsystem 64 mayinclude an overload detector that may determine whether or not a signalderivative of analog audio input signal ANALOG_IN (e.g., an analogsignal output by AFE 56 a) is likely to cause clipping or otherdistortion of digital audio output signal DIGITAL_OUT if a particularaudio processing path (e.g., audio processing path 54 a) is selected. Ifclipping or other distortion of digital audio output signal DIGITAL_OUTis likely if the particular audio processing path (e.g., audioprocessing path 54 a) is selected, control subsystem 64 may generate acontrol signal so that another audio processing path (e.g., audioprocessing path 54 b) is selected. To further illustrate, in someembodiments, audio processing path 54 a may be a path adapted for lowamplitudes of analog audio input signal ANALOG_IN and may thus have ahigh signal gain, while audio processing path 54 b may be a path adaptedfor higher amplitudes of analog audio input signal ANALOG_IN and maythus have a lower signal gain. Thus, if analog audio input signalANALOG_IN or a derivative thereof is greater than a threshold valueindicative of a condition whereby digital audio output signalDIGITAL_OUT may experience clipping or other distortion if audioprocessing path 54 a is selected, control subsystem 64 may detect suchcondition and generate a control signal to select the digital audiosignal generated by audio processing path 54 b as digital audio outputsignal DIGITAL_OUT.

As another example, control subsystem 64 may include a level detectorthat may detect an amplitude of analog audio input signal ANALOG_IN or asignal derivative thereof (e.g., a signal generated within ADC 58 b).Responsive to the amplitude level detected by the level detector,control subsystem 64 may generate the control signal communicated tomultiplexer 60. To illustrate, as analog audio input signal ANALOG_INdecreases from a relatively high amplitude to a lower amplitude, it maycross a threshold amplitude level whereby control subsystem 64 maychange the selection of digital audio output signal DIGITAL_OUT from thedigital audio signal generated by audio processing path 54 b (which maybe adapted for higher amplitudes of analog audio input signal ANALOG_IN)to the digital audio signal generated by audio processing path 54 a(which may be adapted for lower amplitudes of analog audio input signalANALOG_IN). In some embodiments, a threshold amplitude level wherebycontrol subsystem 64 may change the selection of digital audio outputsignal DIGITAL_OUT from the digital audio signal generated by audioprocessing path 54 b to the digital audio signal generated by audioprocessing path 54 a may be lower than another threshold amplitude levelwhereby control subsystem 64 may change the selection of digital audiooutput signal DIGITAL_OUT from the digital audio signal generated byaudio processing path 54 a to the digital audio signal generated byaudio processing path 54 b, in order to provide for hysteresis so thatmultiplexer 60 does not repeatedly switch between the paths.

Each of the various systems described above with respect to FIGS. 2A-4(e.g., audio IC 9A, audio IC 9B, amplifier 18, digital microphone IC 52)may comprise a polymorphic playback system or an integral portionthereof, in that in each of such systems, one or more parameters of asignal path of such polymorphic playback system may be varied based onone or more characteristics of a playback signal processed by the signalpath. Although FIGS. 2A-4 set forth specific examples of a polymorphicplayback system, a polymorphic playback system may include any othertype of system in which one or more parameters of a signal path of suchsystem is varied based on one or more characteristics of a playbacksignal processed by the signal path.

FIG. 5A illustrates a block diagram of selected components of ageneralized polymorphic playback system 70A, in accordance withembodiments of the present disclosure. As shown in FIG. 5A, polymorphicplayback system 70A may filter an input signal with a low-latency filter72, which may then be processed by a polymorphic plant 82 to generate anoutput signal. Polymorphic plant 82 may comprise any system, device, orapparatus in which one or more parameters of a signal path of thepolymorphic playback system are varied based on one or morecharacteristics of a playback signal processed by the signal path. Forexample, polymorphic plant 82 may select between polymorphic modes basedon comparisons of one or more characteristics of the playback signalprocessed by the signal path to one or more thresholds set by thresholdcontrol subsystem 73A and received by polymorphic plant 82.

Threshold control subsystem 73A may be configured to detect anout-of-band noise profile of the input signal by using a noisecharacterization subsystem 74A which may filter the input signal usinghigh-latency filter 76 that performs more robust filtering than filter72, and then, using combiner 78, subtracting the input signal asfiltered by filter 76 from the input signal as filtered by filter 72 togenerate a resulting signal which is an indication of the amount ofout-of-band noise present in the filtered signal received by polymorphicplant 82. Based on this amount of out-of-band noise, a thresholdcalculation block 80A may calculate thresholds. For example, thresholdcalculation block 80A may increase or decrease relevant thresholds basedon the out-of-band noise present. As another example, a range ofhysteresis between a first threshold for switching from a firstpolymorphic mode to a second polymorphic mode, and a second thresholdfor switching from the second polymorphic mode to the first polymorphicmode, may increase for higher levels of out-of-band noise and decreasefor lower levels of out-of-band noise.

FIG. 5B illustrates a block diagram of selected components of anothergeneralized polymorphic playback system 70B, in accordance withembodiments of the present disclosure. As shown in FIG. 5B, polymorphicplayback system 70B may filter an input signal with a low-latency filter72, which may then be processed by a polymorphic plant 82 to generate anoutput signal. Polymorphic plant 82 may comprise any system, device, orapparatus in which one or more parameters of a signal path of thepolymorphic playback system are varied based on one or morecharacteristics of a playback signal processed by the signal path. Forexample, polymorphic plant 82 may select between polymorphic modes basedon comparisons of one or more characteristics of the playback signalprocessed by the signal path to one or more thresholds set by thresholdcontrol subsystem 73B and received by polymorphic plant 82.

Threshold control subsystem 73B may be configured to detect anout-of-band noise profile of the input signal by using a noisecharacterization subsystem 74B which may detect an out-of-band noiseprofile by analyzing statistics associated with the playback signal. Insome embodiments, such statistics may be indicative of a frequency ofoccurrence of the playback signal crossing the one or more playbacksignal magnitude thresholds. To illustrate, increment block 84 anddecrement block 86 may cause a numeric value maintained by a counter 88to increase each time polymorphic plant 82 switches between polymorphicmodes, and compare with comparator 90 the output of counter 88 to alimit to determine if the frequency of switching between polymorphicmodes is greater than the relevant limit. Frequent switching betweenpolymorphic modes may indicate a high level of out-of-bound noise, andthus, the output of comparator 90 may be an indication of the amount ofout-of-band noise present in the filtered signal received by polymorphicplant 82. Based on the signal generated by comparator 90, a thresholdcalculation block 80B may calculate thresholds. For example, thresholdcalculation block 80B may increase or decrease relevant thresholds basedon the out-of-band noise present. As another example, a range ofhysteresis between a first threshold for switching from a firstpolymorphic mode to a second polymorphic mode, and a second thresholdfor switching from the second polymorphic mode to the first polymorphicmode, may increase for higher levels of out-of-band noise and decreasefor lower levels of out-of-band noise.

For the purposes of clarity and exposition, FIG. 5A shows a system usingfiltering to extract an out-of-band noise characterization from theplayback signal and FIG. 5B shows a system that analyzes statisticsassociated with the playback signal to extract an out-of-band noisecharacterization. However, in some embodiments, a polymorphic playbacksystem may utilize both filtering to extract an out-of-band noisecharacterization from the playback signal and statistical analysis ofthe playback signal to extract an out-of-band noise characterization.

Using the systems and methods described above, the setting of the one ormore playback signal magnitude thresholds may minimize switching (e.g.,oscillation) between the polymorphic modes due to out-of-band noise.

As used herein, when two or more elements are referred to as “coupled”to one another, such term indicates that such two or more elements arein electronic communication or mechanical communication, as applicable,whether connected indirectly or directly, with or without interveningelements.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, or component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative. Accordingly, modifications, additions, oromissions may be made to the systems, apparatuses, and methods describedherein without departing from the scope of the disclosure. For example,the components of the systems and apparatuses may be integrated orseparated. Moreover, the operations of the systems and apparatusesdisclosed herein may be performed by more, fewer, or other componentsand the methods described may include more, fewer, or other steps.Additionally, steps may be performed in any suitable order. As used inthis document, “each” refers to each member of a set or each member of asubset of a set.

Although exemplary embodiments are illustrated in the figures anddescribed below, the principles of the present disclosure may beimplemented using any number of techniques, whether currently known ornot. The present disclosure should in no way be limited to the exemplaryimplementations and techniques illustrated in the drawings and describedabove.

Unless otherwise specifically noted, articles depicted in the drawingsare not necessarily drawn to scale.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the disclosureand the concepts contributed by the inventor to furthering the art, andare construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present disclosurehave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

Although specific advantages have been enumerated above, variousembodiments may include some, none, or all of the enumerated advantages.Additionally, other technical advantages may become readily apparent toone of ordinary skill in the art after review of the foregoing figuresand description.

To aid the Patent Office and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims or claimelements to invoke 35 U.S.C. § 112(f) unless the words “means for” or“step for” are explicitly used in the particular claim.

What is claimed is:
 1. A polymorphic playback system wherein one or moreparameters of a signal path of the polymorphic playback system arevaried based on one or more characteristics of a playback signalprocessed by the signal path, comprising a control subsystem configuredto: detect an out-of-band noise profile of the playback signal; and setone or more playback signal magnitude thresholds for switching betweenpolymorphic modes of the polymorphic playback system based on theout-of-band noise profile, wherein the polymorphic modes comprise atleast a first polymorphic mode in which one or more first parameters areapplied to the signal path and a second polymorphic mode in which one ormore second parameters are applied to the signal path.
 2. The system ofclaim 1, wherein the control subsystem is configured to detect theout-of-band noise profile by filtering to extract an out-of-band noisecharacterization from the playback signal.
 3. The system of claim 1,wherein the control subsystem is configured to detect the out-of-bandnoise profile by analyzing statistics associated with the playbacksignal.
 4. The system of claim 3, wherein the statistics are indicativeof a frequency of occurrence of the playback signal crossing the one ormore playback signal magnitude thresholds.
 5. The system of claim 1,wherein the setting of the one or more playback signal magnitudethresholds minimizes switching between the polymorphic modes due toout-of-band noise.
 6. The system of claim 1, wherein the setting of theone or more playback signal magnitude thresholds comprises setting arange of hysteresis between a first threshold for switching from a firstpolymorphic mode to a second polymorphic mode, and a second thresholdfor switching from the second polymorphic mode to the first polymorphicmode such that the range of hysteresis increases for higher levels ofout-of-band noise and decreases for lower levels of out-of-band noise.7. A method for use in a polymorphic playback system wherein one or moreparameters of a signal path of the polymorphic playback system arevaried based on one or more characteristics of a playback signalprocessed by the signal path, comprising: detecting an out-of-band noiseprofile of the playback signal; and setting one or more playback signalmagnitude thresholds for switching between polymorphic modes of thepolymorphic playback system based on the out-of-band noise profile,wherein the polymorphic modes comprise at least a first polymorphic modein which one or more first parameters are applied to the signal path anda second polymorphic mode in which one or more second parameters areapplied to the signal path.
 8. The method of claim 7, wherein a controlsubsystem is configured to detect the out-of-band noise profile byfiltering to extract an out-of-band noise characterization from theplayback signal.
 9. The method of claim 7, wherein a control subsystemis configured to detect the out-of-band noise profile by analyzingstatistics associated with the playback signal.
 10. The method of claim9, wherein the statistics are indicative of a frequency of occurrence ofthe playback signal crossing the one or more playback signal magnitudethresholds.
 11. The method of claim 7, wherein the setting of the one ormore playback signal magnitude thresholds minimizes switching betweenthe polymorphic modes due to out-of-band noise.
 12. The method of claim7, wherein the setting of the one or more playback signal magnitudethresholds comprises setting a range of hysteresis between a firstthreshold for switching from a first polymorphic mode to a secondpolymorphic mode, and a second threshold for switching from the secondpolymorphic mode to the first polymorphic mode such that the range ofhysteresis increases for higher levels of out-of-band noise anddecreases for lower levels of out-of-band noise.